Cheers all, the bike in question is 2003 firemountain, I bought some hydraulic brakes from eBay and they threw in the derailleur, which was nice of them as the brakes turned out to be toss!
Didnt know if it was worth putting on the fm, but I've got a 96 hahanna to build up which has an acera deraileur ?? So at least it will be an upgrade on that